1. Field of the Invention
The present invention relates to a plasma display panel, and more particularly, to a method and apparatus for driving a plasma display panel.
2. Description of the Background Art
A plasma display panel (hereinafter, referred to as “PDP”) is adapted to display an image by light-emitting phosphors with ultraviolet rays generated during the discharge of an inert mixed gas such as He+Xe or He+Xe. This PDP can be easily made thin and large, and it can provide greatly enhanced picture quality with the recent development of the relevant technology. Particularly, a three-electrode AC surface discharge type PDP has advantages of lower driving voltage and longer product lifespan as a wall charge is accumulated on a surface in discharging and electrodes are protected from sputtering caused by discharging.
FIG. 1 is a perspective view illustrating the construction of a discharge cell of a conventional three-electrode AC surface discharge type PDP. Referring now to FIG. 1, the three-electrode AC surface discharge type PDP includes a plurality of scan electrodes Y and a plurality of sustain electrodes Z which are formed on the bottom surface of an upper substrate 10, and an address electrode X formed on a lower substrate 18. The discharge cell of the PDP is formed at every crossing of the scan electrodes Y, the sustain electrodes Z and the address electrodes X and is arranged in a matrix form.
Each of the scan electrode Y and the sustain electrode Z includes a transparent electrode 12, and a metal bus electrode 11 that has a line width smaller than the transparent electrode 12 and is disposed at one side of the transparent electrode. The transparent electrode 12, which is generally made of ITO (indium tin oxide), is formed on the bottom surface of the upper substrate 10. The metal bus electrode 11 is generally formed of a metal on the transparent electrode 12 and serves to reduce a voltage drop caused by the transparent electrode 12 having high resistance. On the bottom surface of the upper substrate 10 in which the scan electrodes Y and the sustain electrodes are disposed is laminated an upper dielectric layer 13 and a protective layer 14. The upper dielectric layer 13 is accumulated with a wall charge generated during plasma discharging. The protective layer 14 is adapted to prevent damages of the electrodes Y and Z and the upper dielectric layer 13 due to sputtering caused during plasma discharging, and improve efficiency of secondary electron emission. As the protective layer 14, magnesium oxide (MgO) is generally used.
The address electrodes X are formed on the lower substrate 18 in the direction that they intersect the scan electrodes Y and the sustain electrodes Z. A lower dielectric layer 17 and a diaphragm 15 are formed on the lower substrate 18. A phosphor layer 16 is formed on the surface of the lower dielectric layer 17 and the diaphragm 15. The phosphor layer 16 is excited with ultraviolet rays generated during the plasma discharging to generate any one visible light of red, green and blue lights. An inert mixed gas such as He+Xe, Ne+Xe or He+Xe+Ne for discharge is injected into the discharge space of the discharge cells provided between the upper and lower substrates 10 and 18 and the diaphragm 15.
Such a three-electrode AC surface discharge type PDP is driven in such a way that one frame is divided into several sub fields of different emission numbers based on an address-display-separated sub field driving system. FIG. 2 shows a conventional one frame containing eight time-divided sub fields. If an image is to be represented using 256 gray levels, a frame period (16.67 ms) corresponding to 1/60 second is divided into 8 sub fields SF1 to SF8, as shown in FIG. 2. Each of the sub fields SF1 to SF8 is divided into a reset period for initializing a discharge cell, an address period for selecting a discharge cell, and a sustain period for implementing the gray level according to the number of discharge. The reset period and the address period of each of the sub fields SF1 to SF8 are the same in every sub fields, whereas the sustain period and its discharge number increase in the ratio of 2n (n=0, 1, 2, 3, 4, 5, 6, 7) in each sub field.
The aforementioned PDP driving method causes picture quality to vary with the order, weight and number of the sub fields. When the PDP driving method is used, motion artifact, large area flicker and a variation in the number of visible gray levels affect the picture quality. The motion artifact is caused by dynamic false contour noise and motion blurring. The dynamic false contour noise appears as a subfield-driven nonlinear emission pattern, and the motion blurring occurs when light is emitted from pixels for a period of time longer than one frame period. The dynamic false contour noise and the number of gray levels (the number of sub fields) or the large area flicker and the motion blurring have a complementary function relationship between them. For example, the motion blurring occurs when a frame frequency is increased in order to reduce flicker whereas severe flicker is generated when the frame frequency is decreased in order to reduce the motion blurring.
Recently, some PDP manufacturers have attempted to improve picture quality deterioration such as the dynamic false contour noise, large area flicker and so on by rearranging sub fields and modulating the frame frequency from 50 Hz to 100 Hz as shown in FIG. 3. In FIG. 3, the vertical axis represents a weight given to each sub field and the horizontal axis represents time. When the method shown in FIG. 3 is employed, large area flicker generated at 50 Hz can be reduced and an emission pattern can be dispersed with a 100 Hz driving method to decrease the dynamic false contour noise. However, the address period and the sustain period become seriously short as resolution is increased to WVGA, XGA or HD resolution so that it is impossible to arrange sub fields at 100 Hz.
Another method for reducing flicker is to make the optical center of the maximum brightness uniform in every frame when the optical center of the maximum brightness is varied with frames in a sub frame array in which weights are linearly arranged. However, this method requires a complicated algorithm and circuit for calculations for making the optical center uniform in every frame.
Furthermore, there is an attempt to remove the dynamic false contour noise using a method of increasing the number of sub fields while varying a panel luminance or a method of increasing the number of sub fields without varying the panel luminance in such a manner that the address period and vertical resolution are exchanged. In this case, however, there is a limitation in increasing the number of sub fields when the resolution of PDP is increased. Furthermore, a vertical data component may be lost due to bit line repeat of a pre-filter.